1. Field of the Invention
The present invention relates to an injection device which comprises:                a needle support;        an injection needle which is fixedly joined to the needle support and which has a free end which is arranged with spacing from the needle support; and        a mechanism for extracting the injection needle, the mechanism comprising a base and a pushing member which can be moved relative to the base between a position in which the needle is used and a position in which the needle is extracted.        
2. Background Art
In some pathological fields, it is necessary to inject daily a liquid dose of medication directly into an organ of a patient. To this end, it is known to permanently implant, in the chest of the patient, a chamber which is arranged beneath the skin. This chamber is extended with a tube which leads from the support to the organ where the dose of medication has to be delivered. The chamber which can be implanted comprises a container which has a cover perforatable along the surface thereof which is in contact with the skin.
In order to inject the dose of medication, the needle of the device is engaged through the skin of the patient into the implantable chamber and the dose of medication is injected into this chamber through the needle.
In order to carry out injections of this type, an injection device is commonly used which comprises a support which is fixedly joined to the needle. The support is extended by a tube, one end of which is connected to the injection needle and the other end of which is provided with a connector which allows the connection of a syringe or a container of a dose of medication to be injected.
In order to extract the needle from the implantable chamber, the practitioner grips the support of the device and pulls the needle out of the support of the patient.
However, since the membrane of the implantable chamber is relatively strong, a significant pulling force must be applied to the needle in order to allow it to be extracted. In order to prevent the patient from being in discomfort owing to the forces applied to the skin by the implantable chamber when the needle is removed, it is known to use an extraction mechanism as described in document FR 2 781 378.
After being fixedly joined to the needle support, the extraction mechanism comprises a base and a pushing member which can be moved along the length of the needle. The extraction mechanism is positioned and fixedly joined to the needle support only immediately before proceeding to remove the needle from the implantable chamber. The extraction mechanism cannot be left permanently since the space occupied by the pushing member which generally extends parallel with the axis of the needle forms a relatively high projection above the support. The pushing member thus protrudes relative to the skin of the patient, preventing a dressing from being readily placed over the injection device. In the same manner, the protruding pushing member impedes the movements of the patient.